1. Technical Field
The present disclosure relates to a method for using carbon nanotube material and, in particular, to a method for using carbon nanotube material having a positive and negative Poisson's ratio.
2. Discussion of the Related Art
When a sample of material is stretched in one direction, it tends to contract (or occasionally, expand) perpendicular to the direction of stretch. Conversely, when a sample of material is compressed in one direction, it tends to expand (or rarely, contract) perpendicular to the direction of compression. This phenomenon is called the Poisson effect. Poisson's ratio v is a measure of the Poisson effect.
Assuming that the material is stretched along the axial direction:
      v    =          -                        ɛ          trans                          ɛ          axial                      ,wherein v is the resulting Poisson's ratio, εtrans is transverse strain (negative for axial tension, positive for axial compression), εaxial is axial strain (positive for axial tension, negative for axial compression).
The Poisson's ratio of a stable, isotropic, linear elastic material cannot be less than −1.0 nor greater than 0.5 due to the requirement that the elastic modulus, the shear modulus and bulk modulus have positive values. Most materials have positive Poisson's ratio values ranging between 0.0 and 0.5. A perfectly incompressible material deformed elastically at small strains would have a Poisson's ratio of exactly 0.5. Most steels and rigid polymers when used within their design limits (before yield) exhibit values of about 0.3, and increasing to 0.5 for post-yield deformation (which occurs largely at constant volume). Rubber has a Poisson's ratio of nearly 0.5.
The Poisson's ratio of cork is close to 0, showing very little lateral expansion when compressed. Some materials, mostly polymer foams, have a negative Poisson's ratio, if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.
What is needed is a method for using a Poisson's ratio carbon nanotube material having both negative and positive Poisson's ratios.